The vacuum, countergravity, shell mold casting process is particularly useful in the making of thin-walled, near-net-shape castings and involves: sealing a bottom-gated mold, having a gas-permeable upper portion, to the mouth of a vacuum chamber such that the chamber confronts the upper portion; immersing the underside of the mold in an underlying melt; and evacuating the chamber to draw melt up into the mold through one or more of the gates in the underside thereof. Such a process is shown in U.S. Pat. No. 4,340,108 wherein the mold comprises a resin-bonded-sand shell having an upper cope portion and a lower drag portion sealingly held to the mouth of the vacuum chamber by means of spring clips. U.S. Pat. No. 4,340,108 seals the mold to the vacuum chamber atop the cope such that the parting line between the mold halves lies outside the vacuum chamber. U.S. Pat. No. 4,632,171 seals the mold to the mouth of the vacuum chamber atop the drag such that the parting line between the cope and drag falls within the vacuum chamber. U.S. Pat. No. 4,658,880 secures the mold to the vacuum chamber by means of a plurality of reciprocable and rotatable shafts having self-tapping threads on the lower ends thereof engaging mounting sites atop the mold. Reversible motors rotate the shafts so as to screw the threads into engagement/disengagement with the mounting sites to mount/demount the mold to/from the vacuum chamber. Screwing of the threads into the mounting sites draws the mold into sealing engagement with the mouth of the vacuum chamber. Chandley, G. D. Automatic Countergravity Casting of Shell Molds, Modern Casting, October 1983, pages 29-31, describes a technique for mounting round molds to a round vacuum chamber wherein the inside surface of the vacuum chamber includes self-tapping threads which screw into the periphery of the round mold. The aforesaid prior art all disclose molds wherein the upper and lower halves are glued together. The gluing process is expensive and time consuming and elimination thereof would improve the efficiency and economics of the process.
It is an object of the present invention to provide improved apparatus for the vacuum, countergravity casting of shell molds including means for mounting the mold to the mouth of the vacuum box while concurrently securing the upper and lower mold portions together without glue. It is a further object of the present invention to provide such improved apparatus with means for automatically controlling the securing of the mold members together while mounting the mold to the vacuum chamber. These and other objects and advantages of the present invention will become more readily apparent from the detailed description thereof which follows.